(1) Field of the Invention.
This invention relates to a method and apparatus for controlling the contrast of a Liquid Crystal Display (LCD) through using computer control.
(2) Background Information.
A negative voltage is generally required to control the contrast of an LCD, with the contrast being very dependent upon the particular operator viewing the display. There is a certain range of contrast which is acceptable to most operators; however, there is a smaller range which is set according to the preference of individual operators.
In one application, the variation in negative voltage being supplied to the LCD to change the contrast may vary from -14.5 Volts to -20.1 Volts. One of the prior art methods of providing for a change in negative voltage for controlling the contrast of the LCD is to provide, initially, a constant or controlled negative voltage and then, vary the controlled negative voltage through using a potentiometer. When the LCD requires a large amount of power to operate it, using a potentiometer tends to waste energy.
Another problem is that the use of a potentiometer, as described above, requires that there be some external control for adjusting the contrast of the LCD.